1. Field of the Invention
The present invention relates to a thin film transistor panel (or TFT panel) of a liquid crystal display device (or LCD), and more specifically, to a method for reducing the resistivity of a repair line in the TFT panel (or active panel).
2. Description of the Background Art
A conventional liquid crystal display device comprises an active panel and a driving circuit. The active panel, as shown in FIG. 1, comprises an upper panel 2 and a lower panel 1 which are arranged to face each other and to be joined together with a liquid crystal material 25 located therebetween. The upper panel 2 comprises a polarizing panel 20, a transparent substrate 22, a color filter 23 and a common electrode 24 all of which are disposed on the transparent substrate 22. The lower panel 1 comprises a polarizing panel 20, a transparent substrate 21, a plurality of gate lines 14 disposed on the transparent substrate 21, a plurality of data lines 15 which are perpendicularly crossed with the gate lines 14 and a pixel electrode 26 and a thin film transistor 16 which are disposed at the intersection portion of the gate lines 14 and the data lines 15. Pads (not shown in FIG. 1) are formed at the ends of the gate lines 14 and the data lines 15 and have a width that is larger than a width of the respective gate and data lines. The lower panel 1 is divided into a displaying area in which the pixel electrode 26 and the thin film transistor 16 are formed and a pad area in which pads connected to the ends of the gate lines 14 and the data lines 15 are formed.
The thin film transistor comprises a gate electrode 31 connected to the gate line 14, a source electrode 32 connected to the data line 15 and a drain electrode 33 connected to the pixel electrode 26. Generally, the gate electrode 31 and the gate line 14 are formed during the same processing step. Also, the data line 15, the source electrode 32 and the drain electrode 33 are formed during the same processing step.
The manufacturing process of the TFT is described with reference to FIGS. 2a-2c. At first, the gate electrode 31 is formed on the transparent substrate 21 of the lower panel 1. An oxidation layer 37 is then formed on the gate electrode 31. Then, an insulating layer 30 is formed so as to cover the gate electrode 31 and the oxidation layer 37. A semiconductor layer 35 is formed on the insulating layer 30 so as to cover the gate electrode 31. An impurity doped semiconductor layer 34 is formed on the semiconductor layer 35. After that, the source electrode 32 and the drain electrode 33 are formed on the doped semiconductor layer 34 and the insulating layer 30. The doped semiconductor layer 34 is patterned by using the source electrode 32 and the drain electrode 33 as a mask. Therefore, the portion of the doped semiconductor layer 34 disposed between the source electrode 32 and the drain electrode 33 is removed. Finally, a passivation layer 36 covering the resulting substrate 21 is formed so that the TFT is completed. The gate line 14 and the gate pad (not shown) are formed at the same time that the gate electrode 31 is formed. The data line 15 and the data pad 40 are formed at the same time that the source electrode 32 and the drain electrode 33 are formed.
In order to increase the resolution of the LCD, many data lines are required. If one data line is broken, then the whole panel can not be used. So, it is necessary prepare an additional line, called a repair line, for repairing a broken line and preventing a broken line from rendering the whole panel unusable. Generally, the repair line is disposed around a periphery of the active panel. The horizontal portion of the repair line is disposed at a location where the gate lines intersect the gate pads and the vertical portion of the repair line is disposed at a location where the data lines intersect the data pads.
FIG. 3a shows the active panel having the data pads 40, data lines 15 and the repair line 60 in detail. FIG. 3b shows another diagram of the active panel according to the conventional art. The repair line 60 comprises a gate line crossing portion 60a and a data line crossing portion 60b. The data line crossing portion 60b of the repair line 60 is formed at the same time that the gate line 14 is formed and the gate line crossing portion 60a of the repair line 60 is formed at the same time that the data line 15 is formed. These two portions of the repair line 60 are connected to each other through a contact hole 51. Referring to the FIG. 3c showing a cross section along the cutting line Axe2x80x94A of FIG. 3a, the manufacturing process of making and connecting the two portions of the repair line 60 in the conventional art is explained.
At first, the data line crossing portion 60b of the repair line 60 is formed at the same time that the gate electrode 31, the gate line 14, the gate pad (not shown) and a common line 70 are formed. Here, the common line 70 which preferably comprises an anti-electrostatic ground line, prevents an electrostatic capacitance from being formed when the gate lines are separated from each other. Then, a gate insulation layer 30 is deposited thereon. The gate insulation layer 30 has a contact hole 51 exposing an end portion of the data line crossing portion 60b of the repair line 60. Then the gate line crossing portion 60a of the repair line 60 is formed at the same time that the source electrode 32, the drain electrode 33, the data line 15 and the data pad 40 are formed. The gate line crossing portion 60a of the repair line 60 is connected to the exposed portion of the data line crossing portion 60b of the repair line 60 through the contact hole 51.
If a data line 15 is broken by a defect 43, then the intersection point 45 of the data line 15 and the repair line 60 is connected. So, the data signal applied to the data line 15 having a defect 43 is detoured through the repair line 60. Hence the broken data line 15 appears to be repaired.
The data line crossing portion 60b of the repair line 60 comprises the same material of the gate electrode 31 and the gate line crossing portion 60a of the repair line 60 comprises the same material as that of the source electrode 32 and the drain electrode 33. So, the data line crossing portion 6b comprises a low resistance metal such as aluminum or copper. On the other hand, the gate line crossing portion 60a comprises a high resistance conductive material such as chromium or indium-tin-oxide (or ITO). Therefore, the resistance of the repair line 60 is related to the sum of the resistance of the two contacts, i.e., the gate material and source material, RG+2Rc+RS/D, where RG is the resistivity of the gate material, Rc is a contact resistance at the data line crossing portion 60b and the gate line crossing portion 60a of the repair line 60 and RS/D is the resistivity of the source material. Hence, the resistance of the repair line 60 is higher than any other part of the active panel.
In this structure, if a data line 15 which is located far from the repair line 60 has a defect 43, then the data line signal traveling the detoured course is significantly delayed by the high resistance of the repair line 60 so that the repair line 60 does not properly work as a repair line. As a result, a repairing area provided by the repair line 60 is limited to only an area located very near to the repair line 60.
To overcome the problems described above, the preferred embodiments of the present invention provide a repair line having a low resistance and having an unlimited or maximum repairing area provided by the low resistance repair line.
According to a preferred embodiment of the present invention, an active panel includes a repair line made of a gate material and a method for manufacturing the same. In the preferred embodiments of the present invention, all parts of the repair line are formed when the gate electrode is formed. Therefore, the repair line comprises low resistance metal such as Al, AlNd, Mo and Cu so that any signal delay occurring at the detoured data line is significantly reduced.
According to preferred embodiments of the present invention, an active panel comprises a display area having a common line and a gate line, a repair line surrounding the display area and crossing the common line, a pad area including a data pad and a gate pad which are located at an area outside of the repair line, wherein the repair line includes a material used to form the gate line.
Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings, wherein like reference numerals indicate like elements to avoid duplicative description.